Development and evolution of depositional systems and the control of tectonic paleogeomorphology of the Dongying Formation in the Northern Liaozhong Depression,Bohai Bay Basin
Based on seismic and well logging data,the types of seismic facies and lithofacies association in the middle and lower part of Dongying Formation in the Northern Liaozhong Depression in northeast of Bohai Bay Basin are identified,and the development and evolution patterns of depositional systems is re-vealed in this study.By flattening the paleo-horizon,the tectonic paleogeomorphology in the sedimenta-ry period of Dongying Formation is restored,the controlling factors of tectonic paleogeomorphology on the development and evolution of depositional systems are discussed.The results show that six types of seismic facies and nine types of lithofacies association can be identified in the middle and lower part of Dongying Formation in the Northern Liaozhong Depression,and develop braided river delta,meandering river delta,sublacustrine fan and clastic lake.Depositional systems in the northern of the study area have evolved from braided river delta to two sides supplied meandering river delta-sublacustrine fan.The small braided river delta developed in the central southern of study area in the early stage and gradually disappeared,and the small braided river delta system in the south gradually advanced to the north.The tectonic paleogeomorphology of the study area is high in the south and low in the north during the depo-sitional periods of the middle and lower part of the Dongying Formation,and can be divided into two patterns,including Liaodong Uplift and Liaozhong Depression.Steep slope break zone,gentle slope fault-step zone,gentle slope zone and valley are further identified.The type and scale of depositional systems developed in the area are closely related to the inclination of the slope break,the location of the subsidence center and the scale of the valley.The distribution and evolution of depositional systems are the results of the joint action of the basin uplift and depression pattern,the slope break paleogeomor-phology,the development location of the valley and the resource supply direction.The results have guiding significance for favorable sand body prediction in the study area.
sedimentary evolutiondepositional systemstectonic paleogeomorphologycontrol factorsmiddle and lower members of the Dongying FormationNorthern Liaozhong DepressionBohai Bay Ba-sin